stop using deprecated python-apt functions

stop using deprecated python-apt functions

Renamed functions and methods:

  Find              -> find
  FindB             -> find_b
  newConfiguration  -> Configuration
  ParseCommandLine  -> parse_commandline
  ParseSrcDepends   -> parse_src_depends
  ReadConfigFileISC -> read_config_file_isc
  SubTree           -> subtree
  ValueList         -> value_list
  VersionCompare    -> version_compare

Removed functions:

  debExtractControl: replaced with utils.deb_extract_control

Other changes:

  x.has_key(y) -> y in x
  x.Find(y)    -> x[y]

The last change was only done in places where `y' is sure to exists (`x.Find'
would return None otherwise, `x[y]' would raise an exception).